1. Field of the Invention
The present invention relates to a speaker device equipped with a crossover network (hereinafter referred to simply as "network") mainly for use in a sound reproducing system on an automobile.
2. Description of the Prior Art
FIG. 2 is a view showing an appearance of a conventional vehicular speaker unit equipped with a network which is disclosed, for example, in Japanese Patent Laid-Open No. 217792/85. FIG. 3 is a view showing the construction of the network portion in the speaker unit illustrated in FIG. 2. Further, FIG. 1 is a circuit diagram showing an example of combination of the speaker unit (tweeter unit) illustrated in FIGS. 2 and 3 with a woofer unit.
In FIG. 1, a capacitor, which corresponds to a capacitor 12b as will be described later, is inserted in series into the tweeter unit to constitute a high-pass filter. An attenuation characteristic of this high-pass filter corresponds to 6 dB/oct, and the capacitance of the capacitor is determined unconditionally by the frequency to be cut off on the basis of the said attenuation characteristic. Generally, a network in a speaker indicates such high-pass filter or a low-pass filter, or a combination thereof. A tweeter unit having a capacitor inserted in series into this circuit is connected in parallel with a woofer unit, and both constitute a speaker system called a two-way speaker system. Many of conventional vehicular speaker systems are relatively simple in structure like the construction of this example.
In FIG. 2, the reference numeral 1 denotes a frame of the speaker unit; numeral 2 denotes a pole piece; numeral 3 denotes a magnet; numeral 4 denotes a terminal strip; numeral 5 a terminal caulked to the terminal strip; numeral 7 a mounting hole formed in the frame 1; numeral 10 a lead wire soldered to the terminal 5; numeral 12 a network unit connected to the lead wire 10; and numeral 11 denotes a lead wire connected between the network unit 12 and a connector unit 13.
In FIG. 3, which illustrates the construction of components of the network unit 12, the numeral 12a denotes a printed circuit board; numeral 12b denotes a capacitor for the network; and numerals 12c and 12d represent electrode patterns formed on the surface of the printed circuit board 12a. The capacitor 12b is connected by soldering between the electrode patterns 12c and 12d. Further, the lead wires 10 and 11 are soldered to the corresponding electrode patterns respectively.
In FIG. 3, moreover, the numeral 12e denotes a connector for applying an audio input signal to the speaker unit, which connector is connected to the lead wire 11. A signal harness on the vehicle side is connected to the connector 12e. Numeral 12f denotes a heat-shrinkable tube. After the capacitor 12b has been soldered to the printed circuit board 12a and subsequently the lead wires 10 and 11 have been soldered to predetermined electrode patterns on the board 12a, the heat-shrinkable tube 12f is used for insulating and fixing all of those components. Numeral 12g denotes a cushion formed of a sheet-like resin foam or the like, which encloses the whole of the network unit in a roll shape.
The cushion 12g is used for preventing a hard component (e.g. printed circuit board 12a) of the network unit 12 from moving, causing collision and making an abnormal noise in the interior of the vehicle during vehicular running. For the same reason, the connector unit 13 is also covered with a cushion material.
The operation of the above conventional speaker unit will be described below.
According to the speaker unit shown in FIG. 2, a high frequency range is reproduced without distortion, and a combination thereof with a woofer unit permits reproduction of high fidelity. More particularly, as to the quality of reproduced sound in a vehicle, there now exists a demand for reproduction of a higher fidelity. For example, a so-called full range type speaker unit which, as a single speaker unit, intends to reproduce the whole range from low to high frequency range has heretofore been used in many cases. According to such a full range type speaker unit, however, a limit is encountered in point of reproduction frequency range and lowering of distortion. On the other hand, according to the speaker unit equipped with a network described above, a multi-channel reproduction can be effected by combining plural speaker units in accordance with reproduction bands and thus a high fidelity reproduction can be realized.
The following description is now provided about a method for mounting the above speaker unit.
FIG. 4 shows an example of a method for mounting the above speaker unit to a vehicle. In the same figure, the numeral 20 denotes an instrument panel of the vehicle; numeral 21 denotes a receptacle space for the speaker unit; numeral 22 denotes a connector; and numeral 23 denotes a signal harness connected to the connector 22. The signal harness 23 extends from an output end of a power amplifier on the vehicular side into the receptacle space 21, in which it shows up. By coupling the connector 22 with the connector 13 of the speaker unit it is made possible to perform sound reproduction. Numeral 24 denotes a bolt for clamping and fixing the speaker unit to the vehicle, and numeral 25 denotes a front glass.
The speaker unit is mounted to the vehicle by first coupling the connector unit 13 with the vehicle-side connector 22, then allowing the entire frame to fall into the receptacle space 21 and thereafter tightening and fixing the bolts 24 to the instrument panel 20 through the mounting holes 7 formed in the frame 1.
Since the conventional speaker unit is constructed as above, there have been the following various problems.
Firstly, it is difficult to install the speaker unit in an optimum place and this has been an obstacle to the reduction of the vehicular manufacturing cost or free design of a vehicle.
In more particular terms, whether the assembling time in the automobile manufacturing process is long or short exerts a great influence on the vehicular manufacturing cost, and hence how to shorten such assembling time has been an important subject. In the case of the conventional vehicular speaker unit equipped with a network and constructed as above, if its external size is large, it is difficult to accommodate the speaker unit into the receptacle space formed on the vehicular side, or even if the receptacle space is capable of receiving the speaker unit therein, the time required for mounting the speaker unit accurately therein may be increased.
This is because there is an optimum installation place which depends on the reproduction frequency of the speaker unit; in other words, it is not that the speaker unit may be installed anywhere in the vehicle. Particularly, a high-pitched sound is sharp in directivity and the attenuation value thereof based on reflection is large, as compared with a low-pitched sound. In a tweeter unit, therefore, it is preferred that the radiation axis of acoustic wave radiated from the tweeter unit be directed to both ears of the driver. For this reason, the tweeter unit is installed on the instrument panel 20 in many cases as shown in FIG. 4.
In the foregoing conventional speaker unit mounted on the instrument panel 20, the lead wires 10, 11, network unit 12 and connector unit 13, which are connected thereto, are bulky and the front glass 25 is an obstacle to widening of the space. Thus, since the installation place is a narrow space difficult to be visually checked, it is difficult to arrange those components in order and such circumstances sometimes cause an obstacle to placing and fixing the speaker unit in a predetermined position.
For example, in the network unit 12, in addition to the size of the printed circuit board 12a, since a non-polarized electrolytic capacitor is usually employed as the capacitor 12b, its external form is bulky. Besides, the printed circuit board with the components thereon is covered with the heat-shrinkable tube 12f which serves as both an insulator and a protector, and the outer periphery of the tube 12f is covered with the cushion 12g made of a soft foamed material, so that the entire external size becomes large inevitably.
When the speaker unit is accommodated in the receptacle space 21 of the instrument panel 20, the components may be buried beneath the pole piece 2 or protrude from the outer peripheral portion of the receptacle space 21, thus making the mounting operation difficult. Further, the components thus covered with the cushion member 12g are bulky and they have been a burden to a rational manufacture of vehicle because two speaker units are generally necessary for stereophonic reproduction.
Consequently, the receptacle space 21 on the vehicle side gives rise to an obstacle which is unignorable in attaining the reduction of the vehicular size. This is because the interior of the vehicular instrument panel 20 is a portion in which are concentrated control devices required for vehicular running as well as indicating instruments essential for vehicular running and typified by speedometer, tachometer and fuel gauge. That is, it has not always been easy to ensure a space for a sound reproducing apparatus having no direct bearing on the vehicular running. Thus, as to the installation place for the tweeter unit, there is antinomy, and how to solve it has been a problem in vehicular design.
Secondly, since the strength of the connecting portion of the network unit 12 is low, disconnection is apt to occur under the action of an external force or the like.
More particularly, the network unit 12 is disposed in a suitable position of the electrical line necessary for transmitting a signal to the speaker unit, but according to the method commonly adopted, as mentioned previously, the capacitor 12b is soldered onto electrode patterns on the printed circuit board 12a, and lead wires are soldered to the printed circuit board, so thus-soldered portions are low in mechanical strength, and the lead wires 10 and 11 are apt to break when an external force such as tension, torsion or bend exceeds a certain limit. Heretofore, such accident of disconnection has occurred most frequently at the time of mounting the speaker unit to a vehicle in the manufacturing process and also due to vibration or impact during vehicular running.
Thirdly, the manufacturing cost of the conventional speaker unit is high and this point has also been an obstacle to the reduction of the vehicular cost.
More particularly, the cost of covering the network unit 12 and the connector unit 13 with the cushion member 12g and that of connecting them with electric wires are also unignorable factors in addition to the manufacturing cost of the speaker unit itself. For example, the cost required for soldering the capacitor 12b to the printed circuit board 12a can be kept relatively low by using an automated manufacturing equipment such as an automatic soldering apparatus, but covering the printed circuit board 12a with capacitor with the cushion member 12g requires manual operation except the case where the production volume is very large. This has been a cause of raising the manufacturing cost.
The reason why manual operation is often adopted is that the external form is not regular so is difficult to be compatible with an automatic machine. In addition, there has been a contradiction such after the printed circuit board has been covered with the cushion member 12g, it is difficult to solder lead wires thereto, while after soldering of leads wires, the printed circuit board is difficult to be compatible with the automatic machine. That is, the problem is that it is impossible to find out an assembling sequence most suitable for the manufacture using an automatic machine. This is a main reason why it has been necessary to adopt a manual assembling work. Besides, it is necessary that the network unit 12 be covered with the heat-shrinkable tube 12f prior to being covered with the cushion member 12g. This has also been a cause of the necessity for adopting manual operation, for the same reason as above.
As an example of a technical literature associated with the prior art there is mentioned Japanese Utility Model Laid-Open No. 4089/85.